Between- and Within-Sex Differences in Body Composition Variables in Professional MMA Fighters and Boxers

Introduction: There is a dearth of data on professional fighters, particularly in mixed martial arts. Thus, this investigation aimed to describe the body composition variables of male and female professional fighters. Methods:  A total of 28 professional fighters participated in this investigation (n=22 male, n=6 female). The majority (68%) of the fighters competed in the Ultimate Fighting Championship (UFC) (n=19). The remaining fighters competed in various other promotions (e.g., WBO, IBF, UFC, Bellator, Eagle FC, Invicta.). Body composition was assessed via dual-energy x-ray absorptiometry (DXA). Total and regional body composition was determined.  Results: There were significant sex differences for Height: Male 180.3 ± 6.7 cm, Female 164.3 ± 6.8 cm (P < .001); Body mass: Male 86.5 ± 11.5 kg, Female 63.3 ± 4.9 kg (P < .001), lean body mass: Male 12.7 ± 2.7 kg, Female 46.7 ± 3.9 kg (P < .001), whole body bone mineral density: Male 1.53 ± 0.13 g/cm2, Female 1.26 ± 0.10 g/cm2 (P < .001), Z-score: Male 2.57 ± 0.88, Female 1.68 ± 1.06 (P < .05), regional bone mineral density (except for the head), regional percent fat (except for the head), and percent body fat; however, no differences were found for age or whole-body fat mass. In males, there was a significant relationship between body mass and lean mass with bone mineral density (p < 0.005, R2 = 0.357). Furthermore, there existed within-sex differences for male fighters. Male fighters' percent fat was significantly different when comparing their left vs. right sides for both the upper and lower extremities. Conclusions: It is evident that profound sex differences exist vis a vis body composition in professional fighters. It should be noted that bone mineral density is exceedingly high in this group of athletes. Furthermore, there tends to be asymmetry in the percent fat of the extremities in male fighters.